1 . Field of the Invention
The present invention relates to a thrust bearing device, and more particularly to such a device that is used in an electric motor, for example, a submersible motor, wherein liquid is contained within the casing thereof to lubricate the thrust bearing device.
2. Prior Art
Heretofore, a thrust bearing device of the type referred to above has involved the use of plural tilting pads, each pad being designed to have a particular configuration such as projecting or inflating in the central region thereof. These pads serve to constitute one of the opposing sliding surfaces. Use of these pads has in turn involved the employment of several related means and many parts which demand additional expense for the installation and maintenance thereof, such maintenance being difficult to carry out.
For example, FIG. 1A illustrates the structure of a typical conventional thrust bearing device in section, FIG. 1B is a fragmentary side view of FIG. 1A, FIG. 1C is a view taken along line 1C--1C of FIG. 1A with the shaft being eliminated for clarification, and FIG. 1D is a view taken along line 1B--1B of FIG. 1A with the shaft being eliminated for clarification.
In this conventional thrust bearing device, the rotary side of the bearing device comprises a rotary disk 101 and a thrust disk 103 adapted to hold in place the rotary disk 101 and attached to a primary shaft 102, while the stationary side of the device comprises a plurality of tilting pads 104 adapted to slidably contact the sliding surface of the rotary disk 101, components for retaining the tilting pads 104, and a complicated alignment mechanism constituted by several components adapted to keep the respective sliding surfaces of the tilting pads 104 coplanar. This stationary side of the bearing device is simply placed on a bracket 107 of the motor.
More specifically, the tilting pads 104 are circumferentially spaced from each other and are placed on a first alignment disk 105-1 through first alignment balls 106-1. An alignment ball 106-1 allows the tilting pad 104 to tilt relative to the disk 105-1 to form a wedge shaped lubricating film between the pad 104 and the sliding surface of the rotary disk 101. Excessive movement of the pads 104 is restrained by pad retainers 105-3 which are disposed so as to engage both sides of each pad. Each pad retainer 105-3 is held in position against the first alignment disk 105-1 by a bearing holder 105-4 which will be explained hereunder. The first alignment disk 105-1 is, in turn, placed on a second alignment disk 105-2 through second alignment balls 106-2 and the second alignment disk 105-2 is in turn, placed on the upper surface of the bracket 107 through third alignment balls 106-3. The second alignment balls 106-2 are disposed along axis-X, whereas the third alignment balls 106-3 are disposed along axis-Y on the X-Y surface of the bearing assembly, as shown in FIG. 1D. The alignment mechanism constituted by these elements 105-1, 105-2, 106-1 to 106-3 allows the tilting of the first alignment disk 105-1, and therefore tilting pads 104, within the X-Y surface of the bearing to compensate for unevenness in height between the sliding surfaces of the tilting pads 104 caused by manufacturing tolerances of the bearing components and thereby keeps the respective sliding surfaces of the tilting pads 104 coplanar. The bearing holders 105-4 extends between the pad retainers 105-3 and the second alignment disk 105-2 and thereby hold all the bearing components in a single assembly.
Each of the sliding surfaces of the tilting pads 104 has a particular shape which is configured as a so-called centrally projected or inflated shape, the center portion being higher than the opposite ends, so that a wedge shaped lubricating film is properly formed between the centrally projected surfaces of the tilting pads 104 and the surface of the rotary disk 101 during the relative rotation therebetween. In this drawing, the reference numeral 108 denotes a radial bearing, 109 a rotor, and 110 a stator.
In the conventional thrust bearing device explained above, however, the following drawbacks may be observed.
(1) The production cost is high since the alignment mechanism constituted by the many components is complicated.
(2) A retaining means constituted by the complicated components is required in order to allow the necessary movement for tilting pads 104.
(3) Fabrication and maintenance are not easy because of the special configuration of the sliding surfaces of the tilting pads 104.
(4) Installation of the thrust bearing device is limited to a particular procedure since the alignment mechanism constituted by the complicated components is not fixed to the motor bracket 107.
(5) The is difficulty in using common components on the rotary and stationary sides.
(6) Maintenance is not easy because of the high precision required of the components constituting the alignment mechanism.